Smelting sulphide ores



Filed Sept. 26, 1950 mill I a.

lNVENTOR fizz world 1? Bacon ATTO RNEYS Patented June 2, 1936 UNITEDSTATES PATENT OFFICE 7 Claims.

This invention relates to the blast furnace smelting of pyrites and hasfor its object the provision of a pyrites smelting process wherein thesulphur liberated is recovered in elemental form.

partly as safety factor in in case of irregularity of than the sulphurdioxide.

As a matter of fact, however, the exit gases in operating the furnaceand also as a result of the more or less open top with which the usualsmelting furnace is run.

In accordance with the process of my invention, the large suchoxidation.

The manner in which I accomplish the same consists in general, inregulating the air fed to the furnace, in slower feeding, in reducingthe sulphur dioxide from the combustion zone by the action of theferrous sulphide (FeS) in the charge, maintaining a non-oxidizingatmosphere in the upper part of the charge to prevent the oxidation ofthe sulphur so reduced as well as that liberated by volatilization, andoperating the furnace with a closed top to prevent the ingress of airabove the charge which would result in oxidation of the elementalsulphur. I also prefer to use a hot blast in my process.

It is to be noted, moreover that this is accomplished and the smeltingoperation carried outas well, with the employment of only the coke orother carbonaceous pyritic smelting; viz. 2 to 6 If reliance were to beplaced upon sulphur dinormal amount of materials used in per cent.

my invention is as follows:

A blast furnace smelter of any well known type, for example the commonwater-jacketed pyritic extending through the water-jackets provide foramount of silica and calclum an iron calcium silicate slag.

To this charge is added a small amount of coke or other suitablecarbonaceous material, primarily to impart suitable porosity to the oreto promote dilfusion, and to an extent, to provide a safety factor inmaintaining the heat in case of earths to provide irregularity ofoperation This function can' likewise be served by any material otherthan coke which will accomplish the same result with- 'the top of thefurnace is its variance upon 2 out interfering with the smelting orrecovering operations.

The amount of coke used will depend upon the physical nature of the oreand the requirements of the particular operation. In general it willvary between approximately 2 and 6 per cent as in ordinary pyriticsmelting, in so far as it is not relied upon to any material extent forfuel value or as a reducing agent for the sulphur dioxide.

The differentiation of my invention from the ordinary pyrites smeltingoperation, is not concerned particularly with the amount of coke usedprovided the use of such coke is limited by the dictates of porositymaintenance and the necessity of providing afuel safety factor.

This charge is introduced into the furnace without the ingress of airduring such operation, and the desired depth of bedis *contrcillsd i -byperiodic additions to the charge as the operation proceeds.

Air is blown in through the tuyeres in the well known manner, and inaccordance with my invention the air blast is introduced at such acontrolled rate that the oxygen will be substantially entirely consumedin the smelting zone, in order to assure the maintenance of asubstantially nonoxidizing atmosphere in the :upper part of the furnace.

.In addition the air blast is introduced atsuch a rate that an elongatedhot zone is produced and the temperature of the furnace is higher in thezone above the tuyere zone than is .usual in-pyritic smelting, this forthe purpose of accelerating the reduction of thesulphur dioxide by theFeS. To further amplify the thermal resources of the process and toassure virtually completeconsumption .of the oxygen in the combustionzone, it is also zdesirable that a very hot blast be used. If desiredthe blast may also be dry, to promote .uniformity of operation and .tofacilitate the attainment of theelongated focus.

As a resulto'f this iproductiono'f an elongated focus, it is desirableto increase the normal height of the charge, :and wherenecessaryasuitably higher furnace should be provided for this purpose.Bysodoing, sufliciently prolonged contact of the sulphur dioxide withthe :iron sulphide will be provided, and an undulyhigh temperature inthe gases escaping from the top of the charge will be avoided. Thetemperature at desirably: held at' 350 to 450 C. V

The most suitable height of charge for the particular ore and operatingconditions can be readily ascertained in each instance by the effect ofthe operation. The-effect, for example, upon the natureof the slag, theconcentration of the matte, and the composition of the exit gases fromthe furnace, particularly as regards their relative sulphur dioxide andfree sulphur contents will serve to indicate the changes which should bemade.

'In-any case,'.lhowever, the charge should not be extended to such aheight that thesulphur would tend to deposit in the furnace as .a resultof :an unduly low top temperature.

'By careful observance of the conditions here- 7 tofore noted, a veryhigh percentage of elemental sulphur will be present in the exit gasesfrom the furnace and the smelting operation will proceed in a markedly.efiectivemanner.

The reactions which take place in the furnace areprobably constituted asfollows:

In the intense combustion zone or focus, the iron and a large proportionof the sulphur in the iron sulphide mixture remaining after the volatilesulphur has been driven off, will be oxidized by the hot air blast withthe formation of sulphur dioxide, an iron calcium silicate slag, and amatte containing the copper or nickel and other values. This matte andslag will descend to the bottom of the furnace, and may be tapped off inthe usual manner.

The hot sulphur dioxide will ascend into the charge, and upon contactingwith the hot iron sulphide will be reduced to elemental sulphur with theaccompanying production of an iron oxide. This reaction probablyproceeds more or less in accordance with one or both of the equations-"In the lower'part of the furnace the first reaction is more likely totake place than the latter, in view of the silica present which .willtend to avidly take up ferrous'oxide at the prevailing high temperatureto form a slag.

Furthermore, the higher v temperature: provided in the elongated focus,will'materially accelerate these reactions, which proceed more rapidlyat higher temperatures. The removal by the silica of the FeO formed,reduces the possibility of the action reversing, and the same is true ofthe velocity of the gas current which will carry the elemental sulphurproduced to the regions where reversing is less likely to'occur.

Proceeding upwardly through thecharge, the reactions will tend toprogress to substantial completion, for a temperature as 'low as'0 'C,is

ordinarily satisfactory for rapid reaction, a requirement amplysatisfied by the attendant smelting conditions.

To further assure the substantial completionof this reducing reactionand particularly. asregards the cooler portion of the chargejIhave'found an intimate admixture of magne's'i'awith the charge to bepeculiarly effective .in catalyzing this reaction, a material reductionin [the necessary temperature being therebyJn'ade possible. In the casewhere magnesia is added to the chargeJas for instance a dolomitic limeit passes into the slag, whose composition will be modified inaccordance with rulesiwell known in the art. 'Lime and iron oxide alsoact as catalystsifor this reaction, but not as effectively as'magnesia.

In the upper portions of the charge the heat ascending from the focusthrough the medium of the gases will volatilize the feeble sulphur atomof the pyrites present in the charge.

Due to the regulation of the air blast to assure consumption ofpractically .all of the oxygen in thecombustion zone, the atmosphere inthe upper part of the charge will be non-oxidizing, and the volatilizedsulphur and that produced by reduc-.

tion of the sulphur dioxide will not'be subjectto oxidation therein.

Furthermore, upon their escape -at the top of the charge, the provisionof the closedtop under which the furnace is operating, -will assure thesubstantial absence of air at the top of the furnace and the exitgaseswill retain theirhigh content of elemental sulphursubstantially-unaffected. 7

Upon discharge from'the' furnace, the gases may be conducted to yafsuitable dust col le'ctor,; for example a mechanical dust separatorsuch :aas-ea bafiie chamber, or an electrostatic i precipita'tor such-asthe well knownCottrellg and 'the dust free gases subsequently conductedthru a fcatalyzer to form sulphur from gaseous sul hur compounds andthen to an apparatus for recovering the sulphur. For this purpose awaste heat boiler or similar cooling means may be utilized to condensethe sulphur and its partial separation may be accomplished therein, orsubsequently by the use of an electrostatic precipitator.

The gases from the dust separation usually contain appreciable amountsof sulphur compounds which warrant further treatment, to recover thesulphur values or remove noxious constituents.

The sulphur compounds which may be present in these gases wouldordinarily consist of S02 and/or H25, and Where carbon wasprovided inthe charge for gas diffusion, a slight amount of COS.

These particular compounds are capable of interaction with theproduction of elemental sulphur according to the equations- Thesereactions are carried out in a catalytic chamber containing a catalyzersuch as porous alumina or bauxite, where they will readily react toyield the additional sulphur in elemental form.

Where insuflicient amounts of sulphur dioxide are present in the gases,supplemental amounts may be added if desired, to carry out theaforenoted reactions, or by slightly increasing the blast the amount ofS02 may be increased.

i'he gases remaining after the final sulphur separation may then bedischarged into the atmosphere, practically entirely freed of theconstituents which ordinarily constitute a very objectionable nuisancein the usual smelting operation.

By proceeding in accordance with the process herein described, manyadvantages are provided over the processes heretofore available.

An economical and very effective recovery of elemental sulphur as anincident to pyrites smelting, is made possible, thereby opening up asubstantial and inexpensive source of this element.

The amount of air necessary calculated on the pyrite is less than halfthat required in the usual pyritic smelting process; and the noxious gasnuisance ordinarily encountered in the operation is entirely eliminated.

The amount of air used in my process is also much less, calculated onthe pyrites charge, than in any process in which coke or coal or othercarbonaceous fuel is used in the furnace in relatively substantialquantity, say 9 to 10 per cent or more. Due to this fact the sulphurcontent of the exit gases is much higher in percentage than in suchprocesses which is a marked advantage of my process, as completelycondensing the sulphur vapor from very dilute hot gases adds cost to aprocess.

The term pyrites as used herein is not intended to be limited to truepyrites, FeSz, but also includes other forms of iron sulphide containingless sulphur than Fesz, for example, pyrrhotite, also iron sulphidescontaining nickel and/or copper, and likewise manufactlured products,such as mattes, which consist principally of iron sulphides. When amaterial of the type of pyrrhotite is smelted, there is little or nofeeble atom of sulphur to be removed by volatilization, hence the zoneof sulphur volatilization is absent; otherwise the operation is much thesame as in the smelting of true pyrites by my process with only suchusual changes in the smelting operation as will be apparent to oneskilled in the art.

I claim:

1. In a process of recovering sulphur from pyrites wherein the pyritesis smelted in a smelting furnace, the steps which comprise, contactingthe sulphur dioxide from the combustion zone with the ferrous sulphidefrom the partially desulphurized pyrites in the presence of a magnesiacatalyst to accelerate the reduction of the sulphur dioxide to elementalsulphur by said sulphide.

2. In a process of recovering sulphur from pyrites wherein the pyritesis smelted in a smelting furnace, the steps which comprise, contactingthe sulphur dioxide from the combustion zone with the ferrous sulphidefrom the partially desulphurized pyrites in the presence of dolomiticlime to accelerate the reduction of the sulphur dioxide to elementalsulphur by said sulphide.

'3. In a process of recovering sulphur from pyrites wherein the pyritesis smelted in a smelting furnace, the steps which comprise, intimatelyadmixing magnesia throughout the pyritic charge to catalyze a reactionof ferrous sulphide upon sulphur dioxide to reduce the latter toelemental sulphur, contacting the sulphur dioxide gases from thecombustion zone first with the hot molten ferrous sulphide of thepartially desulphurized magnesia-containing pyritic charge, and thencontacting said gases with the unmelted ferrous sulphide of saidmagnesia-containing pyritic charge.

4. The process of recovering elemental sulphur from pyrites whichcomprises, subjecting a charge containing the pyrites to the action ofan air blast in a smelting furnace with the blast introduced at such arate that a smelting temperature is attained in the lower portion of thefurnace and the oxygen of the blast is substantially consumed in saidportion, passing the sulphur dioxide produced in such combustion zone incontact with the hot iron sulphide in the charge above the combustionzone for a suitable period of time and with the sulphide provided insuch amount that substantially all of the sulphur dioxide is reduced toelemental sulphur by reaction therewith, 'exeluding oxidizing atmospherefrom above the charge in the furnace, Withdrawing from the furnace thegases issuing from the top of the charge, and separating the elementalsulphur from said gases.

5. The process of recovering sulphur from pyrites which comprises,subjecting a charge containing the pyrites to the action of a hot airblast in a smelting furnace with the blast introduced at such a ratethat a smelting temperature is attained in the lower portion of thefurnace and the oxygen of the blast is substantially consumed in saidportion, passing the sulphur diamount that substantially all of thesulphur dioxide is reduced to elemental sulphur by reaction therewith,excluding air from above the charge during feeding to prevent oxidationof the elemental sulphur, withdrawing from the furnace the gases issuingfrom the top of the charge, and separating the elemental sulphur fromsaid gases.

6. In a process of recovering elemental sulphur from pyrites wherein thepyrites is smelted in a smelting furnace, the steps which comprise,subjecting the lower portion of a charge within the furnace to theaction of a blast of oxidizing gas I5 from pyrites wherein 4 to oxidizethe charge and produce sulphur; dioxide and toemelt the resultingoxidized charge, contacting the sulphur dioxide from the combustion zonein-the furnace with the hot iron sulphide in the upper portion of thecharge in said furnace in the absence of air, and maintaining a suitableamount of iron sulphide in the furnace and suitably prolonging theperiod of contact of the sulphur dioxide with said sulphide tosubstantially completely by reaction therewith reduce the sulphurdioxide furnace, the oxidized charge being withdrawn from the furnace ina molten condition.

.7. In a process of recovering elemental sulphur the'pyrites is smeltedin a smelting'furnacathe steps which comprise, com tacting the sulphurdioxide :fromv the combustion zone and in the absence of air first withthe hot molten iron sulphide of ized pyritic charge, and then contactingthe gases with the unmelted iron sulphide in the upper portion of thefurnace, the contact of the sulphur dioxide with said sulphidebelng'maintained for a suitably prolonged period of time and with thesulphide provided in sufiicient amount to substantially completelyreduce the sulphur dioxide by reaction therewith to elemental sulphurwithin the furnace.

RAYMOND F. BACON.

the partially desulphur-

